继承是面向对象三大特性之一
1、继承的基本语法
语法：
class 子类名 ：继承方式 父类名
子类 也叫 派生类
父类 也叫 基类
class basepage
{
public:
void header()
{
cout << "首页，公开课、登录、注册..." << endl;
}
void footer()
{
cout << "帮助、交流、地图..." << endl;
}
void left()
{
cout << "java、c++、python..." << endl;
}
};
class java : public basepage //继承，减少重复代码
{
public:
void content()
{
cout << "java学科" << endl;
}
};
int main()
{
system("pause");
return 0;
}2、继承方式
继承方式有三种
1、公共继承
2、保护继承
3、私有继承
class basepage1
{
public:
int m_A;
protected:
int m_B;
private:
int m_C;
};
class basepage2
{
public:
int m_A;
protected:
int m_B;
private:
int m_C;
};
class basepage3
{
public:
int m_A;
protected:
int m_B;
private:
int m_C;
};
class son1 : public basepage1 //继承，减少重复代码
{
public:
void func()
{
m_A = 10;
m_B = 20;
//m_C = 30;//报错,父类私有属性不可访问
}
};
class son2 : protected basepage2 //继承，减少重复代码
{
public:
void func()
{
m_A = 10;
m_B = 20;
//m_C = 30;//报错,父类私有属性不可访问
}
};
class son3 : private basepage3 //继承，减少重复代码
{
public:
void func()
{
m_A = 10;
m_B = 20;
//m_C = 30;//报错,父类私有属性不可访问
}
};
void test01()
{
son1 s1;
s1.m_A = 100;//子类公共继承父类公共属性,可访问
//s1.m_B = 200;报错，子类继承父类保护属性，不可访问
}
void test02()
{
son2 s1;
//s1.m_A = 100;//子类保护继承父类公共属性,不可访问
//s1.m_B = 200;报错，子类保护继承父类保护属性，不可访问
}
void test03()
{
son2 s1;
//s1.m_A = 100;//子类私有继承父类公共属性,不可访问
//s1.m_B = 200;//报错，子类私有继承父类保护属性，不可访问
}
int main()
{
system("pause");
return 0;
}3、继承中的对象模型
从父类继承过来的成员，那些属于子类对象？
class basepage1
{
public:
int m_A;
protected:
int m_B;
private:
int m_C;
};
class son1 : public basepage1 //父类中所有的非静态成员属性都会被子类继承下去，包括私有成员
//只是被编译器隐藏了，不可以访问，但是会继承；
{
public:
int m_D;
};
void test01()
{
cout << "size of son1 = " << sizeof(son1) << endl;//sizeof(son1) = 16
}
int main()
{
test01();
system("pause");
return 0;
}4、继承中构造和析构顺序
继承中，先调用父类构造函数，再调用子类构造函数，然后调用子类析构函数，最后调用父类析构函数。
class basepage1
{
public:
basepage1()
{
cout << "base构造函数" << endl;
}
~basepage1()
{
cout << "base析构函数" << endl;
}
int m_A;
protected:
int m_B;
private:
int m_C;
};
class son1 : public basepage1
{
public:
son1()
{
cout << "son构造函数" << endl;
}
~son1()
{
cout << "son析构函数" << endl;
}
public:
int m_D;
};
void test01()
{
son1 s1;
}
int main()
{
test01();
system("pause");
return 0;
}
base构造函数
son构造函数
son析构函数
base析构函数
请按任意键继续. . .
5、继承同名成员处理方式
1、访问子类同名成员，直接访问
2、访问父类同名成员，加作用域
class basepage1
{
public:
basepage1()
{
m_A = 100;
m_B = 300;
}
int m_A;
int m_B;
void func()
{
cout << "base func" << endl;
}
protected:
private:
int m_C;
};
class son1 : public basepage1
{
public:
son1()
{
m_A = 200;
}
void func()
{
cout << "son func" << endl;
}
public:
int m_A;
};
void test01()
{
son1 s1;
cout << "son m_A =" << s1.m_A << endl;
cout << "base m_A = " << s1.basepage1::m_A << endl;
cout << "son m_B = " << s1.basepage1::m_B << endl;
}
void test02()
{
son1 s2;
s2.func();
s2.basepage1::func();
}
int main()
{
test01();
test02();
system("pause");
return 0;
}
son m_A =200
base m_A = 100
son m_B = 300
son func
base func
请按任意键继续. . .6、继承中同名静态成员处理方式
静态成员和非静态成员出现同名，处理方式一样，只不过有两种访问方式，一种通过类名访问
一种通过对象访问。
class basepage1
{
public:
static int m_A;
int m_B;
static void func()
{
cout << "base func" << endl;
}
protected:
private:
int m_C;
};
int basepage1::m_A = 100;
class son1 : public basepage1
{
public:
son1()
{
m_A = 200;
}
static void func()
{
cout << "son func" << endl;
}
public:
static int m_A;
};
int son1::m_A = 200;
void test01()
{
//通过类名访问
cout << son1::m_A << endl;
cout << son1::basepage1::m_A << endl;
//通过对象访问
son1 s1;
cout << "son m_A =" << s1.m_A << endl;
cout << "base m_A = " << s1.basepage1::m_A << endl;
}
void test02()
{
//通过类名访问
son1::func;
son1::basepage1::func;
//通过对象访问
son1 s2;
s2.func();
s2.basepage1::func();
}
int main()
{
test01();
test02();
system("pause");
return 0;
}7、多继承语法
c++允许一个类继承多个类
语法：class 子类名 ：继承方式 父类1，继承方式 父类2，....
多继承可能会引发父类中有同名成员出现，需要加作用域区分
c++实际开发中不建议用多继承
class basepage1
{
public:
int m_A = 200;
int m_B;
void func()
{
cout << "base1 func" << endl;
}
protected:
private:
int m_C;
};
class basepage2
{
public:
int m_A = 300;
int m_B;
void func()
{
cout << "base2 func" << endl;
}
protected:
private:
int m_C;
};
class son1 : public basepage1,public basepage2
{
public:
son1()
{
m_A = 100;
}
void func()
{
cout << "son func" << endl;
}
public:
int m_A;
};
void test01()
{
son1 s1;
cout << "son m_A =" << s1.m_A << endl;
cout << "base1m_A = " << s1.basepage1::m_A << endl;
cout << "base2m_A = " << s1.basepage2::m_A << endl;
}
void test02()
{
son1 s2;
s2.func();
s2.basepage1::func();
s2.basepage2::func();
}
int main()
{
test01();
test02();
system("pause");
return 0;
}8、菱形继承
菱形继承概念：
两个派生类继承同一个基类
又有某个类同时继承两个派生类
这种继承被称为菱形继承，或者钻石继承
class animal
{
public:
int a_age;
};
//继承之前加virtual关键字后，变为虚继承
//此时公共的父类animal称为虚基类
class sheep : virtual public animal
{
};
class tuo : virtual public animal
{
};
class sheepTuo : public sheep,public tuo
{
};
void test01()
{
//此时st中的a_age都是同一个
sheepTuo st;
st.sheep::a_age = 100;
st.tuo::a_age = 200;
cout << "st.sheep::a_age = " << st.sheep::a_age << endl;
cout << "st.tuo::a_age = " << st.tuo::a_age << endl;
cout << "st.a_age = " << st.a_age << endl;
}
int main()
{
test01();
system("pause");
return 0;
}